1. Field of the Invention
The present invention relates to improvements in image-holding member used for holding electrostatic images and/or toner images in electrophotographic image formation process.
2. Description of the Prior Art
Image-holding member is a member on which an electrostatic image and/or a toner image is formed. Electrophotographic photo-sensitive member is one example thereof.
Structure and composition of the electrophotographic photosensitive member vary depending upon the properties required for the member as well as the type of electrophotographic process in which the member is used. Typical electrophotographic photosensitive member now used most widely comprises a support and a photoconductive layer formed thereon. This type of photosensitive member is used for image formation according to the most common electrophotographic process including the steps of electrically charging, image-wise exposure and developing with or without a transferring step.
Sometimes the photosensitive member further comprises an insulating layer as an additional layer serving to protect the photoconductive layer, to improve the mechanical strength of the member, to improve the dark decay characteristic of the member and/or to adapt the member to a particular electrophotographic process. Such photosensitive member comprising an additional insulating layer and the electrophotographic process in which such member is used, are disclosed, for example, in U.S. Pat. No. 2,860,048, Japanese Patent Publication No. 16429/1966 and U.S. Pat. Nos. 3,146,145 (Japanese Patent Publication 15446/1963), 3,607,258 (J.P.P. 3713/1971), 3,666,363 (J.P.P. 23910/1967), 3,734,609 (J.P.P. 24748/1968), 3,457,070 (J.P.P. 19747/1967) and 3,124,456 (J.P.P. 4121/1961).
According to any one of the known electrophotographic processes there is formed on the photosensitive member an electrostatic image which is then developed to visualized the latent image.
Image-holding members other than the above mentioned electrophotographic photosensitive member are also known and used for particular purposes as described hereinafter. These image-holding members comprise no photoconductive layer and are used primarily in the following image forming processes:
(1) Those processes as disclosed in Japanese Patent Publication Nos. 7115/1957, 8204/1957 and 1559/1968. In the process, an electrostatic latent image initially formed on an electrophotographic photosensitive member is transferred to a second image-holding member on which the electrostatic image is developed. The developed toner image is then transferred onto a recording medium. The second image-holding member, that is, a member comprising no photoconductive layer is used to improve the repeating usability of the electrophotographic photosensitive member, that is, the first image-holding member. PA0 (2) Those processes as disclosed in Japanese Patent Publication Nos. 30320/1970 and 5063/1973 and Japanese Patent Application Laid Open No. 341/1976. According to the electrophotographic process, an electrostatic image is initially formed on an electrophotographic photosensitive member in a form of screen having a plurality of fine openings. Though the first electrostatic image, a second electrostatic image is formed on a second image-holding member by treating the second member with corona charge while modulating the ion flow of corona in accordance with the first formed electrostatic image. The second electrostatic image thus formed is developed with toner and the toner image is transferred to a recording medium to obtain a final image as desired. PA0 (3) An electrostatic image forming process in which an electrostatic image is formed by applying electrical signals to needle-electrodes. In accordance with the electrical signals then applied, an electrostatic image is formed on an image-holding member.
The image-holding member used in the electrostatic image forming processes (1)-(3) needs not have any photoconductive layer and is required only to have an electrostatic image holding surface which should be of electrically insulating.
As will be understood from the foregoing, there are various types of image-holding members including the above mentioned electrophotographic photosensitive member and other image-holding members comprising no photoconductive layer. The electrical characteristics which these image-holding members should have are different from each other. However, it is common to all that such image-holding member should have a good durability. Durability is one of the most important properties which all the image-holding members to be used repeatedly should have. It depends upon the durability of image-holding member whether a sharp and clear image can be obtained or not. For the reason, many attempts have been made to improve the durability of image-holding member. As one of the solutions to this problem it has been already proposed to form the insulating layer from curable (setting type) resin (cf. 2533371, i.e. Japanese Patent Application Laid Open Nos. 15441/1976 and 15442/1976). But, there still remains a problem of selection of curable resin most useful for this purpose. Namely, it is an important problem to find out such kind of resin which can form the best durability of insulating layer while improving also other properties of the image-holding member.